Effects of Intrinsic and Orbital Angular Momentum on the Swimming Individual and Relay Starts Performance

There is currently a lack of knowledge about the rotational component of competitive starting techniques using starting blocks equipped with an adjustable back plate and its effect on water entry. The aim of the present study was to examine the angular momentum components of the current competitive swimming starts and to compare the contribution of the body segments to the rotational component of the individual kick start and the relay step start techniques. The block and aerial starting movements of eleven competitive swimmers during an individual and relay start from an Omega OSB11 were filmed at 120 Hz. The total body and the segmental contributions to the intrinsic and orbital components of the angular momentum were computed. Regardless of the type of the start, the orbital rotation of the body segments around the swimmer's centre of mass accounted for a large proportion (between 89 and 91%) of the total angular momentum. At the take-off, the total angular momentum was greater in relay step starts than in individual kick starts (η2 = 0.71). However, the competitive swimmers showed larger lower limb entry angles during the individual kick start (291.5 ± 1.8° vs. 282.2 ± 3.4°), related to a greater segmental contribution of lower limbs (56.5% ± 2.8) to the total angular momentum (η2 = 0.76). The adjustable back plate of the block provided a greater rotational component for the lower limbs in the individual kick start (compared to the relay step start), which assisted swimmers in achieving a better body posture at the water entry.